Kotlin Interview Questions

Frequently asked top Kotlin Interview Questions and Answers with detailed example programs and references. Links would be provided at appropriate junctures in the answers. You may refer those in case you need any clarification. Sequential reading of questions and answers is suggested, as it simulates a kind of interactive session.

Why did you switch to Kotlin from Java ?

Kotlin seems to be simpler and cleaner than Java. It removes a lot of redundancies in code from Java. Kotlin also adds some needed features that Java doesn’t yet support, and is making code more idiomatic. Also Kotlin has been added to Android Studio’s list of supported languages recently. So, there is much to expect from Kotlin in easing out the development efforts and good support in future.

What are the features you think are there in Kotlin but not in Java ?

Kotlin has quite a number of features that Java doesn’t. To name some of them, they are

Extension Functions

Null Safety

Smart casts

Range expressions

Operator Overloading

Data classes

Companion Objects

Coroutines

etc.

What kinds of programming does Kotlin support ?

Kotlin supports two types of programming. They are

Procedural Programming

Object Oriented Programming

What is the entry point to a Kotlin program ? Provide an example.

Like most of the other procedural languages, main() function is the entry point to a Kotlin program.

What are Data classes ? Aren’t they available in Java ? – Kotlin Interview Question

Sometimes we use a class just to hold the data and nothing else. These classes are called Data classes. Of course these kind of classes could be built using Java, but with explicit implementation of getter and setter for each of the properties of class. Also you may need to implement functions like equals, toString and copy separately. What Kotlin does is implementing all these automatically along with special functions called component functions. How cool is that, removing the redundant code bloat.

Ofcourse, Yes. Kotlin uses the concept of extension functions, that we already talked about, to build some useful and more widely used functions among developers directly into the Kotlin library.

Hmm! Where does this Kotlin run ? Does it have some kind of different runtime environment ?

Once compiled, Kotlin programs can run on standard JVM like some other compiled Java code. This means that Kotlin Compiler compiles Kotlin programs to byte-code, which is understood by JVM. So, Kotlin is like a flavor of Java, that goes alongside Java. Interesting fact is that, Kotlin applications can be built with parts of Java code.

So, how do you migrate the code from Java to Kotlin ? – Kotlin Interview Question

JetBrains IDEA provides inbuilt tools to convert Java code to Kotlin code. Then you may do the magic offered by Kotlin at some of the parts in code, to make it clean.

What does init block do and Where does it appear in a class ? – Kotlin Interview Question

What is the difference between val and var ? – Kotlin Interview Question

Val (Value) is like a constant. Once assigned a value, you cannot change it. On the other hand Var (Variable) is designed to be a storage location that can accept reassignment of values of same data type or what ever feasible by the data type casting.

What is Kotlin’s Null Safety ? – Kotlin Interview Question

Null Safety in Kotlin is to eliminate the risk of occurrence of NullPointerException in real time. Kotlin can differentiate between nullable references and non-nullable references. If a variable has to be allowed to store a null value, that has to be declared with a null (?) operator.